The overall objectives of the proposed research are two-fold: (1) to establish at the ultrastructural level the characteristics of the surface membrane of sporozoites of mammalian malaria and (2) to investigate the mode of interaction of these parasites with immune serum, and its effect on parasite-host cell interaction, particularly the uptake of sporozoites by macrophages, and their penetration into liver cells. It is planned to approach the investigation of the morphological characteristics of the surface membrane of sporozoites by means of freeze-fracture electron microscopy; defining the ultrastructural changes resulting from the interaction of antisporozoite antisera, and this parasite stage in an attempt to clarify the mechanism of antibody-induced "sporozoite neutralization" determining the presence and distribution of antigen(s) on the surface membrane of salivary gland sporozoites; defining serum of the cytochemical properties of the surface membrane of sporozoites; futher defining and investigating the in vitro interaction of macrophages obtained from normal, immune and non-specifically stimulated animals with sporozoites preincubated in either normal or immune sera; in addition, investigating, in vitro, the invasion of liver cells by sporozoites using hepatocytic lines maintained in cultures. These investigations should hopefully provide an answer to a number of basic questions on malaria host-parasite interaction.